Retailers use a variety of electronic article surveillance (EAS) tags and corresponding detectors to detect or prevent theft of goods. These EAS tags may be electro-magnetic (EM) tags or acousto-magnetic (AM) tags. Both of these types of tags use the principles of magnetism.
EM tags are made by combining a strip of metal having low magnetic saturation value and a ferromagnetic material having a moderate coercive field. An example of a metal having a low magnetic saturation is an amorphous metal. Detection of an EM tag involves sensing and recognizing signals generated by a non-linear magnetic response by an EM tag exposed to a mixture of low-frequency (e.g., 10-1,000 Hz) magnetic fields.
An EM tag may be deactivated by being demagnetized (e.g., by exposing the EM tag to a magnetic field). The magnetic field biases the amorphous metal strip of the EM tag into saturation such that the EM tag no longer produces harmonics when exposed to a detector emitting the low-frequency magnetic fields and the EM tag can no longer be detected.
Conventionally, detection of an EAS tag is a binary event. That is, a detector determines whether an EAS tag is present or not present at a location near the detector. Other than detection, no information is available from many types of EAS tags.